The present invention relates to a laser shutter mechanism for use in covering a laser beam emission opening of an optical system container containing an optical system having a laser oscillator.
Conventionally, there is known an image recording device utilizing an electrophotographic system in which a surface of a photoconductive drum is exposed to light to form a latent image on the drum surface. Toner is then applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet and is fixed by a fixing unit. Such an image recording device is chiefly employed in a copying machine. In recent years, however, the image recording device has been used in a Printer or the like for printing output from a computer. One such device is a laser beam printer.
The laser beam printer comprises, for example as illustrated in FIG. 1, a photoconductive drum 1. Arranged about the photoconductive drum 1 in order of the rotational direction thereof are a charging station A, an exposure station B, a developing station C, a transferring station D, a toner-cleaning station E, and a discharge station F.
The arrangement is such that at the exposure station B, the laser beam scans the surface of the drum 1, which has been uniformly charged at the charging station A, to thereby form a latent image on the charged drum surface. Toner is then applied at the developing station C to the latent image to develop the same. Subsequently, the developed toner image is transferred at the transferring station D onto the recording sheet P traveled at a velocity identical with the peripheral speed of the photoconductive drum 1. The recording sheet P carrying the toner image transferred there to at the transfer station D is guided and/or conveyed by guide rollers to a fixing station G. The recording paper P is then heated and/or pressed at the fixing station G for the toner image to be fixed on the surface of the recording sheet P.
The construction of the laser beam printer is substantially similar to that of an electronic copying machine except for the exposure station. In fact, principal parts of the electronic copying machine are often commonly used for conventional laser beam printers.
The electronic copying machine is designed so that an image-carrying surface can instantly be viewed by transferring the toner image onto the top surface of the recording sheet and discharging the recording sheet with the image-carrying side up (so-called "faceup discharging"). This naturally results in the faceup discharging system is employed in laser beam printers having principal parts in common with an electronic copying machine.
However, printers are normally used to print out sheets continuously and, if the sheets are discharged with the image-carrying surfaces up, they will be stacked in inverted order of pages. As a result, it is desirable for the laser beam printers to be able to discharge the sheets with their image-carrying surfaces down (so-called "facedown discharging") so the sheets are stacked in the correct order of pages.
What has been heretofore proposed to overcome the above defect is that an electrophotographic printer having a recording sheet feed path as well a fixing station disposed above a photoconductive drum so that an image may be transferred to the undersurface of the recording sheet before being discharged and stacked. In this case, the exposure unit is substantially disposed under the photoconductive drum.
However, the photoconductive drum has to be replaced after its useful life (in terms of the number of sheets) because the photoconductor on the surface thereof wears thin or because a change in electrostatic characteristics results in defective charging or transfer as the photoconductive drum is repeatedly used.
In the case of the transfer unit conventionally disposed above the photoconductive drum, the exposure unit disposed under the photoconductive drum may be exposed to the outside during the replacement of the photoconductive drum. In case the laser oscillator is accidentally actuated in the aforementioned state, the operator will be directly exposed to the laser beam emitted thereform and the laser beam directly sent upon the unprotected eyes of the operator poses a serious problem. Even though a switch for electrically detecting the presence of the photoconductive drum is provided to stop the operation of the power supply when the photoconductive drum is removed, the suspension of the operation thereof is not ensured if the switch is out of order.